In a related art, vapor phase growth of an epitaxial layer onto a main surface of a semiconductor substrate (hereinafter, simply referred as substrate) is performed by disposing a susceptor in a reaction chamber, heating the substrate to a desired growth temperature by a heating apparatus in an arrangement state of the substrate on the susceptor and supplying a reaction gas on the main surface of the substrate by a gas supply apparatus.
When vapor phase growth of an epitaxial layer of low dopant concentration (that is, high resistivity) is performed on a substrate of high dopant concentration (that is, low resistivity), for example, when vapor phase growth of a p-type silicon epitaxial layer (hereinafter, simply referred as epitaxial layer) is performed on a P+-type boron(B)-doped substrate, a phenomenon (hereinafter, referred as autodoping) that dopant once released from inside of the substrate into vapor phase is doped into the epitaxial layer occurs. This autodoping is caused by dopant outdiffused from the substrate by heating and dopant released from inside of the substrate due to vapor phase etching of a surface of the substrate. When autodoping occurs, a problem is arisen that dopant concentration of the epitaxial layer after vapor phase growth increases along a direction from the center to a peripheral edge of the layer (contrarily, in a case of p/p+-type or n/n+-type, resistivity decreases along the direction from the center to the peripheral edge).
In the related art, to prevent an occurrence of such autodoping, in-plane uniformity of dopant concentration (and resistivity) is performed by forming in advance a silicon oxide film (SiO2 film, hereinafter, simply referred as oxide film) on a rear surface of the substrate and by performing vapor phase growth while preventing release of dopant from inside of the substrate due to the oxide film.
However, as described above, when vapor phase growth is performed after forming the oxide film in advance on the rear surface of the substrate, a process for forming the oxide film is required, and productivity deteriorates.
Further, to perform in-plane uniformity of dopant concentration, for example, as shown in Japanese Patent Application Laid Open No. 223545/1998, a vapor phase growth susceptor with a hole penetrating to a rear surface at an outermost peripheral portion of a pocket (concavity formed in an almost substrate shape; wafer pocket in this publication) arranged to place the substrate in a positioning state is proposed. In this susceptor, in-plane resistivity (and dopant concentration) distribution is not improved so much (resistivity in a case of p/p+-type or n/n+-type has in-plane distribution so as to be considerably lowered along a direction from the center to a peripheral edge portion of an epitaxial wafer; referred to data of a susceptor 100 in FIGS. 4, 5 and 6).
This invention has been accomplished to solve the above problem, and an object of this invention is to provide a susceptor, a vapor phase growth apparatus, an epitaxial wafer manufacturing method and an epitaxial wafer in which in-plane uniformity of dopant concentration and resistivity can be easily obtained.
Another object of this invention is to provide a susceptor and epitaxial wafer manufacturing apparatus and method in which in-plane uniformity of resistivity (dopant concentration) of an epitaxial wafer can be easily obtained without forming in advance an oxide film on a rear surface of a substrate.